The present invention relates to an ultrasound treatment apparatus for necrosing a tumor such as a tumor by focusing ultrasound on the tumor.
A great deal of attention has recently been given to MIT (Minimally Invasive Treatment). For example, a ESWL (Extracorporeal Shock Wave Lighotriptor (Lighoripsy)) is available, which destroys a calculus by extracorporeally irradiating the calculus with energy instead of a surgical operation. Such energy is generated by a (submerged) discharge type, electromagnetic (induction) type, small-explosion type, piezoelectric type, and the like. The piezoelectric type, in particular, has the following advantages. For example, energy can be focused to a pinpoint spot, no expendable component is required, energy control is easy, and focal position control is easy (Jpn. Pat. Appln. KOKAI Publication No. 60-145131 and U.S. Pat. No. 4,526,168).
In recent years, a less invasive treatment method which focuses on QOL (Quality Of Life) is receiving a great deal of attention. The mainstream of treatment methods for malignant tumors, i.e., cancers, is constituted by surgery, radiotherapy, and chemotherapy. These treatment methods often accompany the hypofunction of an internal organ and a change in the form of the organ. For this reason, even if the patients life is prolonged, the patient must bear a large burden. QOL is the concept that tries to minimize the burden on the patient after treatment by reducing invasion due to the treatment.
One of cancer treatment techniques capable of realizing QOL is thermotherapy, and more specifically, hyperthermia that uses the difference in heat sensitivity between cancer tissue and normal tissue. In hyperthermia, the tumor (target) temperature is kept at about 42.5xc2x0, which is the necrosis temperature of a cancer cell. Since the necrosis temperature of normal tissue is slightly higher than that of cancer tissue, the normal tissue is not necrosed.
Heating is performed by various method. If heating is performed by using electromagnetic waves such as microwaves, the electromagnetic waves may be deflected by the electrical characteristics of a living body and may necrose normal tissue around the tumor. In addition, the electromagnetic field can hardly reach the deep tumorous region or deep lying region within a body which depth is more than 5 cm from the skin. As a means for solving this problem, a method of inserting a microwave/RF wave antenna into a portion near a tumor has received a great of attention (Isoda et al., J. Microwave Surgery).
Advantageous characteristics of ultrasound are that no surgical operation is required, energy can be focused to a high degree, energy control is easy, and energy can reach relatively deep (Jpn. Pat. Appln. KOKAI Publication No. 61-139551). Recently, a treatment method of necrosing a tumor accompanying thermal coagulation by instantaneously heating the tumor to 80xc2x0 C. or more by using very strong ultrasound whose ultrasound intensity reaches several hundred to several thousand W/cm2 at the focus has been developed (G. Vallancien et al.: Progressin Urol, 1991, 1, 84-88, U.S. Pat. No. 5,150,711).
In this treatment method, since ultrasound is focused to a very high degree to form a very small spot, the focus of ultrasound must be moved to entirely treat a large tumor. For this reason, it is required to improve the positioning precision of the focus with respect to the tumor. To improve the positioning precision, the present inventors have developed a technique of imaging the body temperature distribution by using an MRI (Magnetic Resonance Imaging Apparatus) on the basis of the temperature dependency of chemical shift (Jpn. Pat. Appln. KOKAI Publication No. 5-253192). In addition, a technique of imaging the intensity distribution of treatment ultrasound by receiving the echoes of the treatment ultrasound generated by a treatment ultrasound source with an imaging probe has been developed (U.S. Pat. Nos. 1,851,304, 1,821,772, and 1,765,452). An improvement in positioning precision can be attained by using various techniques, as described above.
In addition to an improvement in positioning precision, another challenge for ultrasound treatment is optimization of the amount of energy injected (ultrasound intensityxc3x97irradiation period). According to the experiment conducted by the present inventors, injection of excessive energy causes destruction of a tissue cell beyond thermal degeneration. In a thermal degenerate state, the tissue cell is necrosed, but it maintains its form. If, however, the tissue cell is destroyed, its original form changes. For this reason, a tumor or neighboring blood vessels may be damaged. As one method of solving this problem, the present inventors have proposed a phase difference driving method of decreasing the ultrasound intensity (focus intensity) at a focus and widening the acoustic field (Japanese Patent Application Nos. 10-278684 and 10-279088). However, optimization rules for focus intensity and irradiation periods could not be established.
As is known, ultrasound energy is absorbed at an acoustic impedance boundary. For this reason, a portion exhibiting a large difference in acoustic impedance, e.g., the body surface of a patient, is unintentionally heated, and may be burnt. There are no appropriate countermeasures against such situations.
Often, a portion near a focus is scanned with an imaging ultrasound probe to acquire B-mode images near the focus so as to check the progress of treatment while strong treatment ultrasound is irradiated. Typically, the frequency of the strong treatment ultrasound is set to 1.6 MHz, whereas the driving frequency of the imaging ultrasound probe is set to 3.7 to 5.0 MHz. The main components of strong treatment ultrasound echoes are not received by the vibrator of the imaging ultrasound probe. However, harmonic components of the echoes are received as noise by the vibrator of the imaging ultrasound probe. Since the noise is much higher in intensity than the imaging ultrasound, the resultant B-mode image becomes almost white. This makes it difficult to observe the tumor.
As a means for solving this problem, Jpn. Pat. Appln. KOKAI Publication Nos. 60-241436, 60-241436, and 10-216145 disclose a technique of stopping irradiation of treatment ultrasound at predetermined intervals, and executing scanning operation using imaging ultrasound only during the stop periods, thereby acquiring B-mode images without noise.
On the other hand, the operator can use almost white B-mode images to visually check whether treatment ultrasound is really irradiated. If, however, scanning operation using imaging ultrasound is executed only during stop periods of treatment ultrasound, the operator cannot visually check whether the treatment ultrasound is really irradiated, although B-mode images without noise can be acquired.
In the arrangements disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 60-241436 and 10-216145, a control signal must be directly input from an ultrasound treatment apparatus to an ultrasound transmitting/receiving section of an ultrasound image diagnostic apparatus or an output must be directly extracted from the ultrasound treatment apparatus. For this reason, if at least a conventional ultrasound treatment apparatus is to be used, the ultrasound transmitting/receiving section inside the apparatus must be modified, or the ultrasound treatment apparatus and the ultrasound image diagnostic apparatus must be integrated. When image information is to be loaded from various image diagnostic apparatuses, e.g., an X-ray image diagnostic apparatus, X-ray CT apparatus, and MRI apparatus, other than an ultrasound treatment apparatus, it is difficult to make modifications for loading of image information with respect to various image diagnostic apparatuses to be combined.
It is an object of the present invention to perform safe, appropriate medical treatment by using an ultrasound treatment apparatus.
According to the present invention, medical treatment is performed under an irradiation condition in which an optimization index obtained by the product of the focus intensity (W/cm2) of treatment ultrasound, the irradiation period (sec) of the treatment ultrasound, and the frequency (MHz) of the treatment ultrasound falls within the appropriate range of 6,000 (inclusive) to 40,000 (inclusive).
According to the present invention, since an irradiation condition is determined on the basis of the focus intensity of treatment ultrasound and the ultrasound intensity in a hyper Echoic region including the body surface of a patient, both optimization of treatment for a tumor and a reduction in damage to the body surface and the like can be attained.
According to the present invention, treatment ultrasound is alternately generated and stopped, and scanning with imaging ultrasound is continuously repeated. B-mode image data sequentially obtained by repetitive scanning are displayed as moving images in real time. B-mode image data corresponding to stop periods of treatment ultrasound are picked up from the B-mode image data sequentially obtained by this repetitive scanning. These picked-up B-mode image data are displayed as skip images. Since a B-mode image during a stop period of treatment ultrasound has an appropriate intensity, the tissue form can be observed. In contrast to this, a B-mode image during a generation period of treatment ultrasound has an excessively high intensity, and hence looks completely white. This makes it impossible to see any tissue form, but allows the operator to determine that treatment ultrasound is indeed irradiated.
In the present invention, treatment ultrasound is alternately generated and stopped, and scanning with imaging ultrasound is intermittently executed in synchronism with stop periods of the treatment ultrasound. Some of scanning periods overlap the generation periods of treatment ultrasound. Therefore, a B-mode image partly looks completely white to hinder the operator from seeing any tissue form. This, however, allows the operator to determine that treatment ultrasound is actually irradiated. In contrast to this, the remaining part of the B-mode image is obtained during a stop period of the treatment ultrasound, and hence is displayed with an appropriate intensity. This allows the operator to observe the tissue form.
According to the present invention, treatment ultrasound is alternately generated and stopped, and scanning with imaging ultrasound is continuously repeated. B-mode image data corresponding to scanning periods which partly overlap stop periods of treatment ultrasound are picked up from the sequentially obtained B-mode image data. Part of a B-mode image therefore looks completely white, and hence does not allow the operator to see any tissue form. This, however, allows the operator to determine that treatment ultrasound is actually irradiated. The remaining part of the B-mode image is obtained during a stop period of the treatment ultrasound, and hence is displayed with an appropriate intensity. This allows the operator to observe the tissue form.
The treatment apparatus of the present invention continuously and externally inputs B-mode image data associated with a cross-section including the focus of treatment ultrasound, picks up B-mode image data corresponding to stop periods of the treatment ultrasound, and displays the data as skip images.
The treatment apparatus of the present invention continuously and externally inputs B-mode image data associated with a cross-section including the focus of treatment ultrasound, picks up the intensity of the focus from the B-mode image data, and displays the intensity as a change over time. The operator can monitor the progress of treatment from this change in intensity over time.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.